Crystal modifier and method for solvent separation of fatty materials

ABSTRACT

CRYSTAL MODIFIERS USEFUL IN THE SEPARATION OF MIXTURES OF MORE SATURATED FROM LESS SATURATED FATTY ACIDS OR MIXTURES OF RELATIVELY SATURATED AND RELATIVELY UNSATURATED TRIGLYCERIDES INTO SATURATED AND UNSATURATED FRACTIONS. ALSO A METHOD FOR CRYSTALLIZATION OF FATTY MATERIALS UNING SAID CRYSTALL MODIEFERS. THE CRYSTAL MODIFIERS ARE PREPARED IN AN ACIDOLYSIS REACTION IN WHICH POLYBASIC ACIDS ARE REACTED WITH FATTY ACID ESTERS OF POLYHYDRIC ALCHOLS.

United States Patent 3,649,657 CRYSTAL MODIFIER AND METHOD FOR SOL- VENT SEPARATION OF FATTY MATERIALS Donald D. Staker and Richard H. Plantholt, Cincinnati,

Ohio, and David J. Kriege, Newport, Ky., assignors to Emery Industries, Inc., Cincinnati, Ohio No Drawing. Filed Apr. 5, 1968, Ser. No. 719,251

Int. Cl. C09f /10 U.S. Cl. 260-419 10 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to crystal modifiers and a method for crystallizing or separating fatty materials. More specifically, it relates to a method for separating more unsaturated fatty materials from less saturated fatty materials. The fatty materials may be in the form of fatty acids or esers such as glycerides.

Naturally occurring triglycerides, whether of animal or vegetable origin, in most instances contain both unsaturated and saturated fatty acid radicals. When the triglycerides are subjected to separating processes to produce free fatty acids, mixtures of saturated and unsaturated fatty acids are produced. The saturated fatty acids have a higher melting point than the unsaturated acid having the same carbon atom content. Because of this difference in melting points and other differences in properties between unsaturated and saturated acids, it is frequently desirable to separate the unsaturated acids from the saturated acids to obtain product fractions having greater commercial utility.

Historically, the most commonly used method of separating unsaturated acids from saturated acids on a commercial scale has been by pressing. The pressing method of separation is performed by cooling a molten mixture of acids without agitation until the mixture is partially solidified, then the resulting mass is enclosed in a porous bag or other filtering medium and subjected to mechanical pressure to force the liquid fraction through the filter medium. The pressing method is, at best, relatively inefiicient in effecting a sharp separation. In order to obtain fractions of desired commercial purity, it is usually necessary to resort to three such cooling and pressing operations to achieve a high purity saturated acid fraction.

Hence, the expression triple-pressed has come to be the conventional term for identifying stearic or other such saturated acids or high purity.

The pressing method, while having been used extensively commercially, has many drawbacks. It requires considerable manual labor, is ineflicient, and diflicult to carry out. As a result, many attempts have been made in the past to effect separation of fatty acids on a continuous basis by other means including selective crystallization from a solvent medium. Generally, selective crystallization processes have been conducted using petroleum hydrocarbons such as propane and hexane or nonhydrocarbon solvents such as acetone and methanol. One of the principal difiiculties with the prior solvent fractionation processes is the crystals formed when a solventfatty material mixture is chilled have been diflicult to filter at commercially practicable concentrations. Moreover, these crystals have included relatively large amounts of occluded unsaturated material and additional stages or crystallization steps have been required to obtain high purity products. In addition, high ratios of solvent to fatty material have been required, necessitating extensive solvent recovery systems, and unless the chilling was performed slowly with gradual crystal growth, a poor separation was obtained with the result that very large refrigerated chilling devices have been required.

The present invention provides an improved crystal modifier which enables highly effective separation of fatty materials or differing degrees of saturation such as stearic acid from oleic acid in a single crystallization step. It also enables the separation to be accomplished at a very low solvent to fatty material ratio thereby improving the economics of the separation process. It further provides a method whereby fatty material crystals are produced which can be easily separated from a solvent medium.

The crystal modifiers of this invention provide improved selective crystallization by promoting a denser type of crystal formation in the stearic acid or other crystallizable fatty material being selectively crystallized and make a more easily filterable and washable filter cake. More important, the use of these materials as crystal modifiers permits the use of higher concentrations of fatty acids in the solvent without any excessive thickness in the crystal slurry resulting, and this permits an increase in production rate for a plant of any given capacity. Without the use of a modifier, concentrations of not more than about 20 to 25% by weight fatty material in solution are feasible; however, when the crystal modifiers of this invention are used, concentrations of from 35 to fatty material in solution may be employed in a plant. The difference in the crystal structure induced by crystal modifier causes a thinner and less slimy and viscous crystal slurry than is formed without a crystal modifier. The slurry is more easily filtered and washed. This permits a higher percent solids in the filter cake and a firmer'c'ake to be o'btained'and reduces the amount of solvent which must be distilled out of the cake.

DESORIPTION OF THE INVENTION 7 i The present invention is concerned with crystal modiacid and oleic acid and glyceride fats and oils. The

method of the invention is particularly applicable to the selective crystallization of saturated fatty acids from mixtures of saturated and unsaturated fatty acids obtained from glyceride materials of animal or vegetable origin, such as tallow or other fats and oils.

The crystal modifiers of this invention are polymeric esters which are prepared by the reaction of a polybasic acid with a fatty acid ester of a polyhydric alcohol.

The invention is practiced by forming a solution of the materials to be separated and the crystal modifier, and then cooling the solution to precipitate out the more saturated constituent.

The polybasic acids which may be used in the preparation of the crystal modifiers of this invention are aliphatic or aromatic polybasic acids, usually dibasic acids and some tribasic acids having from about 6 to about 54 carbon atoms. Specific examples of acids which may be used are phthalic acid, isophthalic acid, terephthalic acid, azelaic acid, adipic acid, sebacic acid, and polymerized fatty acids which are commonly referred to as dimer acid and trimer acid. The latter two types of acids are generally made by polymerizing unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid, and have about 36 and 54 carbon atoms respectively.

The fatty acid esters which are used in the acidolysis reaction employed to prepare the crystal modifiers of the present invention may be glycerides of either animal or vegetable origin such as tallow or other fats and oils. The fatty acid moiety may be a saturated or unsaturated aliphatic fatty acid having from about 8 to 22 carbon atoms and the alcohol moiety may be a polyhydric alcohol having from about 2 to about 6 carbon atoms and from about 2 to about 6 hydroxyl groups. Specific examples of these polyhydric alcohols are ethylene glycol, propylene glycol, erythritol, glycerol, pentaerythritol, and sorbitol. The preferred fatty acid esters both from the standpoints of economics and crystal modifier performance which are produced are glycerides such as hydrogenated tallow and hydrogenated vegetable oils. The preferred polybasic acids for use in the acidolysis reaction to produce the crystal modifiers of this invention are the dibasic dimer acids having about 36 carbon atoms.

2 The amount of polybasic acid which is reacted with the fatty acid ester to produce the crystal modifiers of this invention varies over a wide range and is dependent to a large extent upon the dibasic acid which is employed. Usually from about to 50% by weight of polybasic acid, based on the total weight of the polybasic acid and fatty acid ester reactants, is used. Generally speaking, lesser amounts of the lower molecular weight dibasic acids such as'adipic, azelaic, or phthalic acid are required than dimer acid or trimer acid. The preferred crystal modifiers of this invention are prepared by reacting about 2535% by weight dimer acid with hydrogenated tallow when tallow fatty acids are separated, the amount of dimer acid being based upon the total weight of the dimer and tallow.

The acidolysis reaction is performed by heating the polybasic acid and fatty acid ester in a reaction vessel at a temperature of about 250 to 300 C. usually under reduced .pressure of about 1 to 5 mm. mercury. During the reaction the polybasic acid replaces some of the monobasic acids in the glyceride structure and forms modifiers is not known although they' areb'eIieved to be" higher molecular weight esters containing 2 or more polyol units. The physical form of the modifier is generally a waxy amorphous solid having a higher viscosity than the original mixture. The monobasic acids which are liberated in the reaction may be evaporated and collected by distillation. When approximately 70 to by equivalent weight of the polybasic acid charged is removed intheform of monobasic acids in the distillate, the reaction is considered complete. The reaction may take place fromabout 3 to 24 hours depending upon the temperature used and the polybasic acid and fatty acid esters which are used in the preparation of the crystal modifiers. Shorter and longer periods can be used. Shorter, periods generally produce a less effective modifier and longerperiods than about 24 hours do not enhance the quality of'the modi-fier.

In one preferred embodiment of the present-invention 35% by weight dimer acid based onthe total weight .of dimer acid and hydrogenated tallow is reacted at a temperature of 250 to 300 C. and at a pressure varyingfrom 1 to 5 mm. mercury with the hydrogenated tallow for period of 6 hours. 7

We have found in general that it is desirable to use as the ester reactant, one having as the fatty acid moiety a fatty acid of the same chain length-as the chain length of the fatty acid fraction being crystallized. Inother words, in the separation of stearic acid from oleic acid, it is preferable to use as the fatty acid ester of a polyhydric alcohol in the formation of the crystal modifier, a glyceride such as tallow which contains principally C fatty acids.

The separation process of the present invention is conducted by first forming a solution of the fatty materials which are to be separated into component fractions by selective crystallization. An organic solvent, preferably a polar organic solvent, is employed as a solvent medium. The crystal forming characteristics of the resulting solutions are such that, with most fatty materials, the concentration of fatty material in the starting solution should not exceed about 35 to 50% by weight of the solution if good results are to be obtained during the crystallization and, more particularly, the crystal separation and washing steps. As the fatty material concentration materially exceeds about 50%, the crystal mass formed on cooling the solution tends to become slimy in character and is difficult to handle. Filtering of the crystals is slow, as are subsequent washing steps. Moreover, the washed saturated acid, e.g. stearic acid filter cake, tends to be contaminated with an undue proportion of unsaturated acids, e.g. oleic acid. Further processing may be required if the oleic acid content is too high. The ratio by weight of solvent to fatty material can vary over a range of about 1:1 to about 3:1, with the lower solvent to fatty material ratios being preferred.

After the solution of the fatty material to be separated into its component fractions and modifier has been formed, the solution is chilled. The amount of crystal modifier to be employed will normally range from about 0.2 to 3% based on the weight of fatty material present in the solution, with a preferred range being from 0.5 to 1.5% by weight. Amounts greater than 3% byweight of crystal modifier can be employed successfully; however, increasing the amount of crystal modifier to such levels provides little if any benefit over and above results which are obtainable at 3% or less. a I

The actual separation of the fatty material into its component fractions is carried out by chilling the solution containing a crystal modifier to a temperature .below the precipitation temperature of the saturated fatty material in the solvent. A sharp separation of the saturated fatty material occurs, the saturated material precipitating in the form of readily filterable crystals.

The separation can be effectively performed in a scraped surface heat exchanger such as the type sold under the tradename Votator. In this type of heat exchanger, the solution is rapidly chilled from a temperature of as high as 35 C. to a temperature at which the more saturated fatty material precipitates in the form of crystals, usually a temperature of about -l C. The precipitated crystals are collected on a filter forming a filter cake and then are washed by solvent. The filter cake is collected and evaporated leaving the saturated fatty material.

The unsaturated components of the fatty material mixture remain in solution and are collected as a filtrate. 10 temperature of 250 C 6 about 35 mm. mercury for hours. The monobasic acids which were formed during the reaction were then stripped at a pressure of l to 5 mm. mercury and at a temperature of 250300 C. The crystal modifier shown in Example 18 was prepared by reacting the adipic acid and hydrogenated tallow for 4 hours under a carbon dioxide blanket at 240 C. The monobasic acids formed in that acidolysis reaction were stripped at the end of the 4 hour period at a pressure of 1 to 5 mm. mercury and at a TABLE L-PREPARATION 0F CRYSTAL MODIFIERS Percent by Polybaslc Fatty acid ester of polyhydric alcohol wt. of

acid polybasic acid Time of weight, Wt., based on total reaction, grams Type grams Type wt. of reactants ours 335 Hydrogenated tallow 35 4 375 -do 25 4 300 do 50 800 Hydrogenated stearic acid residue 1 l0 2. 5 800 Hydrogenated stearic acid residue 2O 5. 5 900 do 10 3 l0 6 10 9 950 do 5 5 400 Hydrogenated tallow 33 8 345 do 12.5 6 309 .do 21 6 400 Coconut oil 6 335 0 ve oil a 33 3 500 Mixed glyceride 4 18 4 288 Ethylene glycol distearate... l5 5 850 Hydrogenated tallow 18 6 66 320 do 17 4 1 Dimer acid used was Empol 1018, a polymerized tail oil fatty acid having about 83% by Weight Cat dibasic acid and about 17%.

by weight 0 4 tribasic acid.

1 Stearic acid residue is a mixture containing predominantly monoglycerides, diglycerides, triglycerides and polymerized gly cerides plus small amounts of stearic acid remaining as residue after the distillation of stearic acid.

1 The trimer acid used was Empol 1040, a polymerized tall oil fatty acid having about 80-90% by weight C tribasic acid and 10-20% by Weight Cat dibasic acid.

4 A mixture of monoglycerides, 50% diglycerides, and 25% triglycerides.

Evaporation of the filtrate enables recovery of the unsaturated components.

As was indicated above, the solvent used in the separation process of this invention should be an organic solvent, preferably a polar organic solvent. A number of solvents may be employed including low molecular weight alcohols, ketones, nitroalkanes, esters, nitriles, amides, and hydrocarbons. Specific examples of solvents which are useful in the present invention are methanol, ethanol, acetone, Z-nitropropane, l-nitropropane, isopropyl acetate, acetonitrile, dimethyl formamide and hexane. The preferred solvent depends upon the fatty material to be separated and the specific method of separation. For most purposes, methanol is preferred with acetone being the next most preferred solvent.

The following examples are provided to further illustrate the invention, but are not be construed as limitative of the scope thereof.

Examples 1 to 18 A number of crystal modifiers of this invention were prepared in an acidolysis reaction by reacting polybasic acids with fatty acid esters of polyhydric alcohols. The acidolysis reaction was performed by charging the polybasic acid and fatty acid ester of a polyhydric alcohol into a reaction vessel and heating the reactants for an extended period of time of from about 3 to 10 hours. During the reaction, monobasic acid was liberated and it was removed from the reaction and collected by distillation.

The reactions for the most part were conducted at temperatures ranging from about 250-300" C., the lower temperature range being generally used initially with the temperature being allowed to increase as the reaction progressed. In Example No. 15, in which phthalic anhydride and a mixed glyceride were used to prepare the crystal modifier, a solvent toluene, was used to aid the reaction. The crystal modifier shown in Example 17 was prepared by reacting the azelaic acid and hydrogenated tallow at a temperature of 250 C. and at a pressure of Examples 19 to 51 A number of tests were conducted to determine the effectiveness of the crystal modifiers shown in Table I in the separation of fatty acid mixtures into their component fractions. The results of these tests are shown in Table II. The crystal modifier type shown in Table II refers to the example number of the modifier shown in Table I. The tests were conducted by first forming a solution of a fatty acid mixture, the crystal modifier, an a solvent, either methanol, acetone or 2-nitropropane. The resulting solution was then cooled in a stirred, scraping crystallizer to from about 0 C. to about 2'0 C. depending upon the solvent and the fatty material to be removed. The resulting slurries were then filtered using a Buchner Funnel while maintaining a vacuum of 5 psi. until no liquid layer was visible above the crystalline layer. The resulting filter cake was then washed using 200 parts by weight of the solvent which was used to form the solution for each parts of the solid cake in the funnel.

Various tests were run on the washed filter cake to determine (1) its content of solids. (2) its yield, and (3) the iodine value of the filter cake solids. The solvent was removed by heating on a steam bath followed by drying on a hot plate. A high solids content in the cake is desirable, for this indicates a correspondingly low content of solvent to be evaporated and returned to the crystallizer unit. One of the most significant features of this invention is the high percentage of solids in cake which are achievable. A low iodine value is desirable because it indicates the effectiveness of the separation process, a low content of occluded unsaturated acid in the washed and dried solids fraction showing good separation. In the runs involving separation of tallow fatty acids, an iodine value of approximately 8-11 is regarded as satisfactory, through the values obtained in plant use might run somewhat higher (or lower), depending upon the nature of the equipment employed, and the severity of the washing step(s).

TABLE II Percent Amount Percent yield Crystal crystal Percent by wt. of more modifier Filtration modifier by wt. fatty saturated from temp. used in of solids material component Iodine Example Number Table I Feedstock Solvent 0.) wt. percent in cake in solution by wt. value 1 Undlstllled PFA I Methanol 1 --l0 1 69. 67 3 Undlstllled PFA Methanol. 1U 51. 8 1 Hydrogenated tall oil 3 .-d0--. 10 1 54. 3 1 Undistllled PFA -1o 0. 5 62. 1 1 1. 5 63. 7 l0 1 44. 8 10 1 41. 5 10 None 26. 0 10 1 61. 0 10 1 34. 2 1 63. 6 ---20 1 46. 0 0 None 17. 4 0 l 21. 1 -l0 1 21. 1 l0 1 51. 8 l0 1 59. 3 l2 1 32. 0 10 1 57. 7 10 1 69. 4 -10 1 47. 3 1O 1 65. 2 -10 1 69. 8 l0 1 68. 4 -10 1 65. 3 10 1 32. 5 1[) 1 61. 2 -10 1 54. 7 10 l 63. 3 -10 1 47. 5 10 1 64. 2 -10 1 65. 0 l0 1 38. 4

1 Pressure split fatty acids. Hydrogenated 153110?- 9 92.5% by weight methanol, 7.5% water. B The C fatty acid distillate recovered irom polymerization oi tall 011 iatty acids.

From the data presented in Table II above, it may be seen that the crystal modifiers of the present invention enable the use of solutions having a far greater concentration of fatty acid than would otherwise be possible, while still obtaining a solid phase which filters well, is high in solids content, has a good yield, and has a desirably low iodine value.

The present process can also be used in the separation of unsaturated acids such as oleic acid from more unsaturated acids such as linoleic acid or linolenic acid, and it is useful in the separation of more saturated fractions from less saturated fractions of glycerides and like materials.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore, only those limitations should be imposed as are indicated in the appended claims.

We claim:

1. A method of promoting the formation of readily filterable crystalline solid fatty materials upon cooling a solution of a fatty material mixture in a solvent of a predetermined temperature which comprises incorporating in the solution of mixed materials a small percentage of a crystal modifier comprising the reaction product of a polybasic acid having from about 6 to about 54 carbon atoms and an ester of a polyhydric alcohol and a fatty acid, said fatty acid having from about 8 to 22 carbon atoms.

2. A process for separating a more saturated fatty material from a less saturated fatty material which comprises forming a solution of said fatty materials and a small amount of a crystal modifier comprising the reaction product of a polybasic acid having from about 6 to 54 carbon atoms and an ester of a polyhydric alcohol and a fatty acid, said fatty acid having from about 8 to 22 carbon atoms, cooling said solution to a temperature sufiicicntly low that said more saturated fatty material precipitates in such solution and recovering the precipitated fatty matcrial and removing occluded solvent therefrom.

5 Hydrogenated stearic acid residue. 6 2-nitro-propane.

3. The process of claim 2 wherein a polar organic sol vent is used to form said solution.

4. The process of claim 2 wherein said more saturated fatty material is stearic acid and said less unsaturated fatty material is oleic acid.

5. The process of claim 2 wherein said fatty materials are glycerides.

6. The process of claim 2 wherein said more saturated fatty material is oleic acid and said less saturated fatty material is linoleic acid.

7. The method of claim 2 wherein said polybasic acid is selected from the group consisting of adipic acid, sebacic acid, pththalic acid, azelaic acid, and polymerized unsaturated fatty acids.

8. The process of claim 7 wherein said polybasic acid is a polymerized unsaturated fatty acid having from 36 to 54 carbon atoms.

9. The process of claim 7 wherein said polyhydric alcohol has from about 2 to about 6 carbon atoms and from about 2 to about 6 hydroxyl groups.

10. The process of claim 9 wherein said polyhydric alcohol is glycerol and said polybasic acid is a polymerized unsaturated fatty acid having 36 to 54 carbon atoms.

References Cited UNITED STATES PATENTS 3,173,935 3/1965 Singleton 260-4l9 3,290,340 12/ 1966 Woo ton 260404.8 3,360,533 12/1967 Wootton 260-428 LEWIS GOTTS, Primary Examiner E. G. LOVE, Assistant Examiner US. Cl. X.R. 

